Nanoengineering of eco-friendly silver nanoparticles using five different plant extracts and development of cost-effective phenol nanosensor

The production of environmentally friendly silver nanoparticles (AgNPs) has aroused the interest of the scientific community due to their wide applications mainly in the field of environmental pollution detection and water quality monitoring. Here, for the first time, five plant leaf extracts were used for the synthesis of AgNPs such as Basil, Geranium, Eucalyptus, Melia, and Ruta by a simple and eco-friendly method. Stable AgNPs were obtained by adding a silver nitrate (AgNO3) solution with the leaves extract as reducers, stabilizers and cappers. Only, within ten minutes of reaction, the yellow mixture changed to brown due to the reduction of Ag+ ions to Ag atoms. The optical, structural, and morphology characteristics of synthesized AgNPs were determined using a full technique like UV–visible spectroscopy, FTIR spectrum, XRD, EDX spectroscopy, and the SEM. Thus, Melia azedarach was found to exhibit smaller nanoparticles (AgNPs-M), which would be interesting for electrochemical application. So, a highly sensitive electrochemical sensor based on AgNPs-M modified GCE for phenol determination in water samples was developed, indicating that the AgNPs-M displayed good electrocatalytic activity. The developed sensor showed good sensing performances: a high sensitivity, a low LOD of 0.42 µM and good stability with a lifetime of about one month, as well as a good selectivity towards BPA and CC (with a deviation less than 10%) especially for nanoplastics analysis in the water contained in plastics bottles. The obtained results are repeatable and reproducible with RSDs of 5.49% and 3.18% respectively. Besides, our developed sensor was successfully applied for the determination of phenol in tap and mineral water samples. The proposed new approach is highly recommended to develop a simple, cost effective, ecofriendly, and highly sensitive sensor for the electrochemical detection of phenol which can further broaden the applications of green silver NPs.

Modification of Cu2+ in polyphenol oxidase extract from purple eggplant for phenol degradation in coal wastewater treatment

Cracking coal-forming organic compounds during the gasification process produces liquid waste containing phenolic compounds that require special handling based on their toxicity. As one of the components, there is liquid waste resulting from the coal gasification process. The purpose of this research was to study the activity of polyphenol oxidase (PPO) on phenol after the addition of Cu2+ to purple eggplant (Solanum melongena L.) extract and its potential to work more effectively in phenol biodegradation for coal wastewater containing phenol. Enzyme activity and phenol determination were carried out spectrophotometrically. The results showed PPO activity of 25.90-38.10 U/mL; 4.0 mM phenol and the activity of PPO-Cu2+ was 21.58-46.32 U/mL; 2-10 mM CuSO4; 2.0-4.0 mM phenol. Based on Michaelis Menten’s graph, the initial rate of PPO-Cu2+ was 0.015 mM/min and the initial rate of PPO was 0.15 mM/min using 2 mM phenol as a substrate. Lineweaver-Burk’s graph shows the KM of PPO-Cu2+ = 6.92 mM, which is lower than KM of PPO = 13.05 mM. Its means that the phenol response has a higher affinity for PPO-Cu2+ than PPO. The application of PPO-Cu2+ in purple eggplant extract works effectively as much as 46.7% for artificial coal liquid waste containing phenol.

Development and certification of reference standards for phenolic content in biologicals, based on comparison of results obtained by GLC, HPLC, spectrophotometric, and colorimetric methods

Phenol is used as a preservative in a number of biological products. Methods that are used for quantitative determination of phenol differ a lot. Current requirements for accredited laboratories include continuous internal quality control. Reference standards with a certified content of the analyte are an effective metrological tool for ensuring such control. The aim of the study was to develop and certify reference standards for phenolic content in biological products, based on comparison of results obtained by GLC, HPLC, spectrophotometric, and colorimetric methods. Materials and methods: diluent for allergens by (candidate reference standard), 2.5 and 5 mg/mL phenol solutions, and 2.5 mg/mL 2-phenoxyethanol solution were used in the study. The experiments were performed using spectrophotometric, colorimetric, HPLC, and GLC procedures. The statistical analysis of results included calculation of the arithmetic mean, standard deviation, coefficient of variation, and analysis of variance with Student’s t-test and Fisher’s F-test. Results: the results of phenolic content determination by the spectrophotometric, colorimetric, and HPLC methods were statistically comparable. The F value obtained for equal sample sizes (n = 40) was F = 0.9343, given the critical value Fcrit = 3.96. A reference standard certified by one of these methods can be used to control the consistency of phenol determination by a relevant method. The results of phenolic content determination by the GLC method showed statistically significantly differences: F = 17.47, given Fcrit = 3.96, which demonstrated the need for certification of another reference standard. Conclusions: two reference standards were certified in the study: reference standard 42-28-449 with the certified phenolic content of 2.56‒3.32 mg/mL, to be used with the spectrophotometric, colorimetric, and HPLC methods; and reference standard 42-28-451 with the certified phenolic content of 2.92‒3.28 mg/mL, to be used with the GLC method.

Au/CeO2/g-C3N4 Nanocomposite Modified Electrode as Electrochemical Sensor for the Determination of Phenol

A convenient and simple phenol electrochemical sensor was constructed based on the Au/CeO2/ g-C3N4 nanocomposites, which were obtained by loading the gold–cerium oxide (Au/CeO2) nanoparticle on graphite-like carbon nitride (g-C3N4) through precipitation–reduction methods. The microstructure and morphology of Au/CeO2/g-C3N4 nanocomposite were verified using different techniques such as XRD, TEM, and HRTEM. Voltammetry and amperometry methods were used to study the electrochemical performance of the constructed phenol electrochemical sensors. The results demonstrated evidently that the combination of Au/CeO2 and g-C3N4 may improve sensing performances of phenol determination. The detection linear range of the sensor was 10–90 μM under the optimum parameters. The Au/CeO2/g-C3N4 based electrochemical sensor also has low detection limits (2.33 μM) and high sensitivities (0.1080 mA/μM) for phenol detection. In addition, the sensor also had considerably favorable anti-interference performance. As a consequence, the sensor demonstrated that the electrochemical system provided a promising effective strategy for detection of phenol.

Infrared spectroscopy for carboxylic acid and phenol determination in biocrude and its derived products

A feasible tool for determination of TAN and carboxylic/phenolic compound content (molar and wt%) was developed based on IR analysis of biocrude oil and its derived upgraded products as well as their distillation cuts.

Highly sensitive biosensing of phenol based on the adsorption of the phenol enzymatic oxidation product on the surface of an electrochemically reduced graphene oxide-modified electrode

An electrochemically reduced graphene oxide and horseradish peroxidase enzyme modified electrode has been used for phenol determination.